Large-gain low-voltage and wideband organic photodetectors via unbalanced charge transport

Gain photodetectors offer large photoresponse towards small optical signals. Despite having achieved high external quantum efficiency (EQE), current gain organic photodetectors (OPDs) generally suffer from narrow spectral sensitivity, slow response time and/or large operating voltage for achieving a favorable gain. So far, strategies tackling one of these issues have often meant sacrificing another parameter. Here, we present solution-processed all-rounder gain OPDs simultaneously featuring broadband activity (300-1200 nm), low-voltage operation and a fast response speed applicable in real-time heath monitoring. A systematic study shows that the gain mechanism stems from adding a small quantity of tetracyanoquinodimethane (TCNQ), which leads to unbalanced charge transport between holes and electrons. The strategy is also transferrable to other organic bulk heterojunction systems, indicating its promising versatility for further exploration.